1. Field of the Invention
The present invention relates generally to an electron emission device, and more particularly to an electron emission display device which has a plurality of electron emission devices arranged in an image display array, for example, in a matrix form.
2. Description of the Related Art
Conventionally, in field electron emission display apparatuses, a Field Emission Display (FED) is known as a planar emission display device equipped with an array of cold cathode electron emission sources which does not require cathode heating. The emission principle of, for example, an FED using Spindt-type cold cathodes of minute protrusions is as follows. Its emission principle is like a Cathode Ray Tube (CRT), although this FED has a cathode array of Spindt-type protrusions which is different from that of CRT. In the FED, electrons are drawn into a vacuum space by means of each gate electrode spaced apart from the Spindt-type cathode, and the electrons are made to impinge upon the fluorescent substance that is coated on a transparent anode, thereby causing light emission.
This FED, however, has a problem of low production yield because the manufacture of the minute Spindt-type emitter arrays as a cold cathode is complex and involves many processes.
There is also known an electron emission device with electron emission devices of metal-insulator-metal (MIM) structure as a planar electron emission source. The electron emission device with the MIM structure comprises an Al underlayer as a base electrode, an Al2O3 insulator layer with about 10 nm thickness, and a Au overlayer, as a top electrode with about 10 nm thickness which are formed in order on the substrate. In the case that this MIM device is placed under an opposing electrode in a vacuum, when a voltage is applied between the Al underlayer and the Au overlayer and, at the same time, an acceleration voltage is applied to the opposing electrode, then some of electrons emit out of the Au overlayer and reach the opposing electrode.
However, even the electron emission device with the MIM structure does not yet provide a sufficient amount of emitted electrons.
To overcome these disadvantages of emission of the MIM device, it is conventionally considered that there is a necessity to make the Al2O3 insulator layer thinner by about several nanometers and make the Al2O3 insulator layer with a uniform quality so that the interface between the Al2O3 insulator layer and the Au overlayer is more uniform.
To provide a thinner and more uniform insulator layer, for example, an attempt has been made to control the anodized current by using an anodization method thereby to improve the electron emission characteristics, as in the invention described in Japanese Patent Application kokai No. Hei 7-65710.
However, even an electron emission device with the MIM structure which is manufactured by this anodization method ensures an emission current of about 1xc3x9710xe2x88x925 A/cm2 and an electron emission efficiency of about 1xc3x9710xe2x88x923.
Furthermore, for application of the electron emission device to various practical embodiments, it is necessary to seal the electron emission device with a high vacuum by using a heating treatment. Therefore the electron emission device will be subjected to the heating treatment under a high temperature at 300 to 500 centigrade degrees. Such a high temperature during the heating treatment increases the electric resistance of layer in the device to make the electron emission characteristic of the device inferior.
The present invention has been made in view of the above circumstances, and thus an object thereof is to provide an electron emission device having an electron emitting efficiency high enough to stably emit electrons at a low voltage applied thereto, and moreover a display apparatus including a flat panel display device which employs a plurality of such electron emission devices.
Moreover another object of the present invention is to provide an electron emission device capable of restricting the increase of the electric resistance of layer caused by the heating treatment.
The present invention provides an electron emission device which comprises:
an electron-supply layer made of semiconductor;
an insulator layer formed on the electron-supply layer; and
a thin-film metal electrode formed on the insulator layer,
characterized in that said electron-supply layer is essentially composed of elements belonging to group IV and has an additive of at least one material selected from atomic elements belonging to group III or V, whereby the electron emission device emits electrons when an electric field is applied between the electron-supply layer and the thin-film metal.
According to the electron emission device having the structure mentioned above, said insulator layer is made of dielectric and has a film thickness of 50 nm or greater.
According to the electron emission device having the structure mentioned above, said additive is included at a ratio ranging from 0.1 to 10 atm % in the electron-supply layer.
The present invention further provides an electron emission display device which comprises:
a pair of a first substrate and an optically transparent second substrate opposing to each other with a vacuum space interposed therebetween;
a plurality of electron emission devices formed on said first substrate, each of which including an electron-supply layer made of semiconductor formed on ohmic electrodes formed on said first substrate, an insulator layer formed on said electron-supply layer, and a thin-film metal electrode formed on said insulator layer and facing the vacuum space, wherein said electron-supply layer is essentially composed of elements belonging to group IV and has an additive of at least one material selected from atomic elements belonging to group III or V;
a collector electrode formed on said second substrate; and
a fluorescent material layer formed on said collector electrode and facing the vacuum space.
In the electron emission display device according to the invention, said insulator layer is made of dielectric and has a film thickness of 50 nm or greater.
In the electron emission display device according to the invention, said additive is included at a ratio ranging from 0.1 to 10 atm % in the electron-supply layer.
In the electron emission display device according to the invention, the display device further comprises plural insulative support members formed on said first substrate and disposed between adjacent ones of said electron emission devices so as to enclose the electron emission devices for partitioning them, wherein the distance from said first substrate to the surfaces of said insulative support members proximate to said vacuum space is substantially equal to the distance from said first substrate to the surface of said thin-film metal electrodes proximate to said vacuum space.
In the electron emission display device according to the invention, the display device further comprises a plurality of bus electrodes, each of which is arranged in a stripe form to electrically connect adjacent ones of said thin-film metal electrodes, wherein said ohmic electrodes and said electrodes are stripe-like electrodes and arranged to extend perpendicular to each other.
In the electron emission display device according to the invention, said first substrate includes a plurality of first insulative ramparts, each of which disposed between said electron emission devices and protruding into said vacuum space, whereas said second substrate includes a plurality of second ramparts each of which protrudes into said vacuum space to abut to said first ramparts.
According to the electron emission device of the invention with the above structure, the device comprises an electron-supply layer made of semiconductor, particularly elements belonging to group IV and having an additive of at least one material selected from atomic elements belonging to group III or V in the periodic table such as boron (B), phosphorus (P), to arsenic (As), antimony (Sb) and so on. Therefore, even when the plural electron emission devices used in a flat panel display device are subjected to a high temperature atmosphere in the manufacturing process, the devices can keep their properties before and after the heating treatment without thermal deterioration due to the high temperature.
Moreover, through-bores are not likely to be produced in the insulator layer because of its relatively thick thickness and therefore its production yield is improved. The electron emission device of the invention is a planar or spot-like electron emission diode and can be adapted to high speed devices such as a source of a pixel vacuum tube or bulb, an electron emission source of a scanning or transmission electron microscope, a vacuum-micro electronics device and the like. In addition, this electron emission device can serve as a minute microwave tube or a diode which emits electromagnetic waves with millimeter or sub-millimeter wavelength, and also can serve as a high speed switching device.